This invention relates generally to the field of vascular occlusion devices and methods. More specifically, it relates to an apparatus and method for occluding a blood vessel by embolizing a targeted site (such as an aneurysm) in the blood vessel.
The embolization of blood vessels is desired in a number of clinical situations. For example, vascular embolization has been used to control vascular bleeding, to occlude the blood supply to tumors, and to occlude vascular aneurysms, particularly intracranial aneurysms. In recent years, vascular embolization for the treatment of aneurysms has received much attention. Several different treatment modalities have been employed in the prior art. U.S. Pat. No. 4,819,637—Dormandy, Jr. et al., for example, describes a vascular embolization system that employs a detachable balloon delivered to the aneurysm site by an intravascular catheter. The balloon is carried into the aneurysm at the tip of the catheter, and it is inflated inside the aneurysm with a solidifying fluid (typically a polymerizable resin or gel) to occlude the aneurysm. The balloon is then detached from the catheter by gentle traction on the catheter. While the balloon-type embolization device can provide an effective occlusion of many types of aneurysms, it is difficult to retrieve or move after the solidifying fluid sets, and it is difficult to visualize unless it is filled with a contrast material. Furthermore, there are risks of balloon rupture during inflation and of premature detachment of the balloon from the catheter.
Another approach is the direct injection of a liquid polymer embolic agent into the vascular site to be occluded. One type of liquid polymer used in the direct injection technique is a rapidly polymerizing liquid, such as a cyanoacrylate resin, particularly isobutyl cyanoacrylate, that is delivered to the target site as a liquid, and then is polymerized in situ. Alternatively, a liquid polymer that is precipitated at the target site from a carrier solution has been used. An example of this type of embolic agent is a cellulose acetate polymer mixed with bismuth trioxide and dissolved in dimethyl sulfoxide (DMSO). Another type is ethylene glycol copolymer dissolved in DMSO. On contact with blood, the DMSO diffuses out, and the polymer precipitates out and rapidly hardens into an embolic mass that conforms to the shape of the aneurysm. Other examples of materials used in this “direct injection” method are disclosed in the following U.S. Pat. No. 4,551,132—Pásztor et al.; U.S. Pat. No. 4,795,741—Leshchiner et al.; U.S. Pat. No. 5,525,334—Ito et al.; and U.S. Pat. No. 5,580,568—Greffet al.
The direct injection of liquid polymer embolic agents has proven difficult in practice. For example, migration of the polymeric material from the aneurysm and into the adjacent blood vessel has presented a problem. In addition, visualization of the embolization material requires that a contrasting agent be mixed with it, and selecting embolization materials and contrasting agents that are mutually compatible may result in performance compromises that are less than optimal. Furthermore, precise control of the deployment of the polymeric embolization material is difficult, leading to the risk of improper placement and/or premature solidification of the material. Moreover, once the embolization material is deployed and solidified, it is difficult to move or retrieve.
Another approach that has shown promise is the use of thrombogenic microcoils. These microcoils may be made of a biocompatible metal alloy (typically platinum and tungsten) or a suitable polymer. If made of metal, the coil may be provided with Dacron fibers to increase thrombogenicity. The coil is deployed through a microcatheter to the vascular site. Examples of microcoils are disclosed in the following U.S. Pat. No. 4,994,069—Ritchart et al.; U.S. Pat. No. 5,122,136—Guglielmi et al.; U.S. Pat. No. 5,133,731—Butler et al.; U.S. Pat. No. 5,226,911—Chee et al.; U.S. Pat. No. 5,304,194—Chee et al.; U.S. Pat. No. 5,312,415—Palermo; U.S. Pat. No. 5,382,259—Phelps et al.; U.S. Pat. No. 5,382,260—Dormandy, Jr. et al.; U.S. Pat. No. 5,476,472—Dormandy, Jr. et al.; U.S. Pat. No. 5,578,074—Mirigian; U.S. Pat. No. 5,582,619—Ken; U.S. Pat. No. 5,624,461—Mariant; U.S. Pat. No. 5,639,277—Mariant et al.; U.S. Pat. No. 5,658,308—Snyder; U.S. Pat. No. 5,690,667—Gia; U.S. Pat. No. 5,690,671—McGurk et al.; U.S. Pat. No. 5,700,258—Mirigian et al.; U.S. Pat. No. 5,718,711—Berenstein et al.; U.S. Pat. No. 5,891,058—Taki et al.; U.S. Pat. No. 6,013,084—Ken et al.; U.S. Pat. No. 6,015,424—Rosenbluth et al.; and Des. 427,680—Mariant et al.
While many prior art microcoil devices have met with some success in treating small aneurysms with relatively narrow necks, it has been recognized that the most commonly used microcoil vaso-occlusive devices achieve less than satisfactory results in wide-necked aneurysms, particularly in the cerebrum. This has led to the development of three-dimensional microcoil devices, such as those disclosed in U.S. Pat. No. 5,645,558—Horton; U.S. Pat. No. 5,911,731—Pham et al.; and U.S. Pat. No. 5,957,948—Mariant (the latter two being in a class of devices known as “three-dimensional Guglielmi detachable coils”, or “3D-GDC's”). See, e.g., Tan et al., “The Feasibility of Three-Dimensional Guglielmi Detachable Coil for Embolisation of Wide Neck Cerebral Aneurysms,” Interventional Neuroradiology, Vol. 6, pp. 53–57 (June, 2000); Cloft et al., “Use of Three-Dimensional Guglielmi Detachable Coils in the Treatment of Wide-necked Cerebral Aneurysms,” American Journal of Neuroradiology, Vol. 21, pp. 1312–1314 (August, 2000).
The typical three-dimensional microcoil is formed from a length of wire that is formed first into a primary configuration of a helical coil, and then into a secondary configuration that is one of a variety of three-dimensional shapes. The minimum energy state of this type of microcoil is its three-dimensional secondary configuration. When deployed inside an aneurysm, these devices assume a three-dimensional configuration, typically a somewhat spherical configuration, that is at or slightly greater than, the minimum energy state of the secondary configuration. Because the overall dimensions of these devices in their non-minimum energy state configuration is approximately equal to or smaller than the interior dimensions of the aneurysm, there is nothing to constrain the device from shifting or tumbling within the aneurysm due to blood flow dynamics.
In some of these three-dimensional devices (e.g., U.S. Pat. 5,122,136—Guglielmi et al.), the secondary configuration is itself a helix or some similar form that defines a longitudinal axis. Devices with what may be termed a “longitudinal” secondary configuration form a three-dimensional non-minimum energy state configuration when deployed inside an aneurysm, but, once deployed, they have displayed a tendency to revert to their minimum energy state configurations. This, in turn, results in compaction due to “coin stacking” (i.e., returning to the secondary helical configuration), thereby allowing recanalization of the aneurysm.
There has thus been a long-felt, but as yet unsatisfied need for a microcoil vaso-occlusive device that has the advantages of many of the prior art microcoil devices, but that can be used effectively to treat aneurysms of many different sizes configurations, and in particular those with large neck widths. It would be advantageous for such a device to be compatible for use with existing guidewire and microcatheter microcoil delivery mechanisms, and to be capable of being manufactured at costs comparable with those of prior art microcoil devices.